Watermelon is an important horticultural crop that accounts for 2% of the world area devoted to vegetable crops. There were 6,024,000 acres of watermelon grown in the world and 187,000 acres of watermelons grown in the United States in 1997 (FAO Production Yearbook 51, 1998). The estimated annual world watermelon value exceeded $7.6 billion when using the United States average price for 1995–1997. The United States watermelon crop amounted to over 41 million cwt, from over 174,000 harvested acres, and a farm value of over $266 million, accounted for 9.2% of the harvested acres, 10.0% of the production, and 3.5% of the value of the United States fresh vegetable industry in 1999 (USDA Agricultural Statistics 2001). California was the leading state in watermelon farm gate value, exceeded $72 million in 2000, due to high percentage of triploid seedless watermelon grown in California. Seedless watermelon receives well above the average price for seeded watermelons in the market.
The goal of plant breeding is to combine in a single variety or hybrid various desirable traits. Desirable traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, and maturity, are important. Other desired traits may include particular nutrient content, color, fruit shape, as well as taste characteristics.
As with many different plants, watermelon contains a fruit part and a plant part. Each part contains different traits that are desired by consumers and/or growers, including such traits as flavor, texture, disease resistance, and appearance traits such as shape and color. The seedless trait in the watermelon fruit is highly desired by consumers. For production of seedless watermelon, optimum pollination characteristics of the pollinating plant are desired.
Seedless watermelon plants are triploid and must be pollinated by the pollen of diploid watermelon plants. To provide adequate pollinization of seedless watermelon plants, it is current practice to plant diploid pollenizer plants over approximately 25–33% of the field surface. The remaining portion of the field is planted with the triploid plants. Thus, to maximize the value of the crop in the field, growers use high yield marketable diploid watermelon varieties, which ultimately compete with the triploid seedless varieties for sun, nutrients, and space.
A pollenizer for seedless watermelon producing small and unmarketable fruits, which are not harvested, has been disclosed (WO00/70933). However, when this pollenizer is used, a lower total yield of marketable fruit is observed when compared to a commercial pollenizer line. Also, the fruits of the pollenizer described in WO00/70933 that are not harvested become hosts for diseases in the future, and their seeds will germinate and grow into weeds, thus reducing future yields.
The present invention recognizes the need to increase the yield of the seedless watermelon, preferably without loss in total yields of marketable fruits. The present invention also recognizes that novel phenotypic characteristics of the diploid pollenizer plants are needed to permit these diploids to be planted in close proximity to the triploid plants and to share the field surface with the triploid plants, thereby effectively decreasing the surface area of the field required for the diploid pollenizers of the invention. The present invention also recognizes the need to minimize the carryover of unharvested pollenizer fruits as weeds into the subsequent season. The present invention also recognizes the need to increase the pollenizing capacity of diploid watermelon plants in order to further decrease the ratio of diploid to triploid plants in the field, thereby also increasing the yield of the seedless watermelon. The present invention also further recognizes the needs to allow farmers to distinguish the seedless fruits from the fruits of the pollenizer in the field and to provide marketable value to the pollenizer fruits themselves.